Ah, I simply misunderstood what you said in your post about dry and wet signals. Now that I read it with emphasis (in bold),
"...you would run into problems when mixing the wet _and the dry_ signals from different Venues."
I understand that with "dry signals" you mean the dry part of the wet signal. In relation to this, the MIR Pro manual on page 52 says: "Using the Wet Solo button in the Output Channel you will hear no direct signals at all". To avoid confusion, when you press the "Dry Solo" button in MIR you will hear the direct signal. What causes confusion so often is that there are so many different words for these concepts: source, orginal, direct and dry signal, early reflections, late reflections, stage reflections, late reflections, tail....
Yet I agree completely, that is, if I do correctly understand you now ;-) Indeed, mixing different sets of early reflections can throw our psychoacoustical localisation system in disarray, I experienced that before with all kinds of reverberators, as well as mixing multi-mic'ed live recordings, where carefully adjusting pre-delays can work wonders.